BLOWING COLD AIR THEN NOT BLOWING COLD AIR

Hello
My 2002 XC Volvo will blow cold air then it will jsut stop. The air still blows, and its cool jsut not cold. Eventualy its almost like jsut having the vent on. If you turn the system off then back on in a few minutes it will sometimes work. I know there is some kind of fresh air sensor for the AC could that be bad? Help its getting Hot in Atlanta!